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Transmission

P0720 — Output Speed Sensor Circuit

The ECU or TCM does not get a valid signal from the transmission output speed sensor. Without it the transmission cannot judge vehicle speed properly, so shifting and the speedometer may be wrong.

Severity: Medium

Common causes

  • Faulty output speed sensor
  • Damaged wiring or connector
  • Dirty or low transmission fluid, debris on the sensor
  • Damaged tone ring or gearbox fault
  • Control module fault (rare)

Symptoms

  • Speedometer not working or erratic
  • Harsh, delayed or missing shifts
  • Limp mode
  • Check engine light

How to check

  1. Check the transmission fluid level and condition
  2. Inspect the sensor connector and wiring
  3. Compare output speed with vehicle speed on a scan tool
  4. Replace the sensor; inspect the gearbox if debris is found

Can you keep driving?

Avoid long trips. Drive only as far as needed to reach a workshop.

Frequently asked questions

What does P0720 mean?
The transmission output speed sensor is not giving a valid signal.
Why does the speedometer fail with P0720?
On many vehicles it uses the output speed sensor signal.

General reference information. It does not replace a diagnosis on your own vehicle. The same code can have different causes depending on make, model year and engine; check the manufacturer's documentation or ask a technician with a scan tool.